1. Field of the Invention
This invention relates to automatic transmission control system and control method, and in particular to an automatic transmission control system capable of performing shift control in an automatic shift mode and a manual shift mode and such an automatic transmission control method.
2. Description of the Related Art
A known automatic transmission control system has an automatic shift mode in which shifting of the automatic transmission is controlled based on a shift diagram, and a manual shift mode in which shifting of the automatic transmission is controlled in accordance with upshifting and downshifting operations performed by the driver. If the driver performs an upshifting or downshifting operation during running of the vehicle in the automatic shift mode, the control system switches from the automatic shift mode to the manual shift mode, and the automatic transmission is shifted up or down in accordance with the driver's operation. An example of the control system as described above is disclosed in Japanese Patent Application Publication No. 11-257485 (JP-A-11-257485).
In the known automatic transmission control system as disclosed in JP-A-11-257485, an upshift switch and a downshift switch are mounted on a steering wheel so as to enable the driver to perform upshifting and downshifting operations, and the driver can press down the upshift switch and downshift switch on the steering wheel. If the driver presses down the downshift switch so as to apply an engine brake, the control system switches from the automatic shift mode to the manual shift mode, and effects downshift of the automatic transmission in response to the driver's operation.
In the known automatic transmission control system, when a specified time elapses after the downshift switch is pressed down, the system is arranged to switch from the manual shift mode to the automatic shift mode in which shifting is controlled based on the shift diagram. Thus, shift control of the automatic transmission based on the shift diagram, which is not intended by the driver, may be undesirably carried out upon the lapse of the specified time from the time that the downshift switch is pressed down. For example, even in the case where the automatic transmission is shifted down according to the driver's operation on the downshift switch, and the driver wishes to keep the transmission in the downshifted condition, the system switches from the manual shift mode to the automatic shift mode when the specified time elapses after the driver presses down the downshift switch, and the transmission may be switched back to the original gear position even though the driver caused the transmission to be shifted down. More specifically, even if the driver operates the downshift switch before the vehicle enters a curve so as to reduce the speed of the vehicle, the control system switches back to the automatic shift mode after a lapse of a given time, and effects upshift of the transmission based on the shift diagram while the vehicle is turning along the curve, which may result in a spin of the vehicle.
Also, in the known automatic transmission control system, switching from the automatic shift mode to the manual shift mode takes place when the driver presses down the downshift switch or upshift switch. Therefore, in the case where the driver wishes to simply switch the system from the automatic shift mode to the manual shift mode, the driver is required to press down the downshift switch or upshift switch, resulting in downshift or upshift of the transmission which is not desired nor intended by the driver.
Thus, in some cases, the known automatic transmission control system performs shift control of the automatic transmission in a manner that is not intended by the driver, which may result in deterioration of driveability.